1. Field of the Invention
This invention relates to an electric control system including at least two electrical control devices and a mechanical interlock therebetween preventing both control devices from simultaneously assuming a closed or "ON" position. More particularly, the instant invention interlocks two circuit interrupters and prevents the switching of one of the interrupters to the "ON" position while the other interrupter is "ON".
2. Description of the Prior Art
Pivoted beam type mechanical interlocks have been used between two circuit interrupters to prevent both interrupters from being in their closed or "ON" position simultaneously. The circuit interrupters each include a stationary contact and a movable contact and blade. Each interrupter also includes a plunger extending through an opening in the circuit interrupter housing which is associated with the movable contact blade such that the plunger is pushed to an outward position when the contacts are in a closed position and is returned, or is free to be returned, to its original or inward position when the contacts are opened.
The circuit interrupters are positioned such that the plungers engage the beam on opposite sides of the pivot whereby the extended plunger of one circuit interrupter pivots the beam to prevent extension of the plunger of a second circuit interrupter thereby preventing the second interrupter from assuming a contact closed position while the first interrupter is closed.
Another type of interlock which will be referred to as a walking beam interlock is illustrated in U.S. Pat. No. 3,303,300, issued Feb. 7, 1967 and assigned by the inventor, Merlin Y. Turnbull, to the assignee of the present invention. The beams of this interlock are pivotally connected to levers near opposite ends, which levers are then pivotally connected to the plunger assembly of the interlocked circuit interrupters.
The pivoted and walking beam interlock assemblies are essentially restricted for use with circuit interrupters positioned in side by side relationship. The length of the beam also dictates the spacing of the associated circuit interrupters.
Furthermore, the pivoted or walking beam interlocks are not appropriate for use with circuit interrupters having three independent sets of main contacts with a common trigger linkage that provides for simultaneous opening or closing operations. If one set of contacts in a three pole circuit interrupter should weld closed and the common triggering linkage should happen to operate to open the contacts, only two sets of contacts would open while the welded contacts would remain closed. An effective interlock system must be provided which will prevent the closing of a second circuit interrupter while any of a number of poles of a first circuit interrupter remains closed. The interlock system must be effective irrespective of the number of poles in each of the circuit interrupters.